Physics of the Japanese Car Pack DLC

I see this one is available for purchase now too, so here are some notes on those cars.

Datsun 280ZX Turbo AAGT: You guys are gonna like this one; it’s a total hot rod. There’s not a ton of historical data for it as reliability issues kinda hindered its racing career, but we can look past that and just let it run strong as it did at its best.

AAGT was IMSA's take on Group 5-style regulations to get some new, interesting cars entered in the series. It allowed any engine to be installed in any chassis so long as they were from the same manufacturer. So here we have a 4.2L V8 from the Nissan President Limo, tweaked and tuned with the biggest turbo they could find. The lazy, 200hp road car engine ends up here with something in the range of 940hp@7500rpm when using full qualifying boost pressure of 36psi. It was good for 208mph at Daytona, fastest in a straight line in a field which included a number of Porsche 935 K3s.

Other than that, it wasn't the greatest car to be honest (hence the short racing career). Suspension is basic struts at the front and simple wishbones at the rear; nothing fancy but it makes for predictable handling. Power runs to the rear through a 5-speed Hewland and ZF-type clutch & plate differential; I expect they at least experimented with a spool to help put down the huge power in a predictable manner, like in the 935s. Aero additions with that massive bodywork on the rear end are mainly to help with high speed stability. I’m sure it was good for modest net downforce on the rear, but overall this thing was dominated by aero drag. Weight was 200kg heavier than a Porsche 935, so it didn't corner particularly well and it burns through tires quickly. But, man, is it a hoot to drive and it can hang pretty well on tracks that favor top speed.

Honda Civic Type-R: Nothing too fancy here other than being a well-polished FWD hot hatch design. It's a lot like the Megane RS275 with 30hp more and independent rear suspension, or like the A1 quattro with 50hp more and FWD only. Fun, fast little car. 310hp doesn’t sound like a lot these days, but it arrives in a useful manner and the 6-speed manual is geared so each ratio is properly spread for track use; no extra-long highway gear on this one. It is prone to the usual FWD behavior when driven hard and pushing the 235 rubber - a bit of torque steer, a bit more lift-off oversteer. Personal best here so far is a 7:53 at the Ring on sticky semi-slick tires, so that real world target of 7:43 is surely in reach for the faster drivers amongst you all.

Nissan Skyline GT-R BNR32 Group A: Godzilla, right? The fundamentals of this car are actually quite similar to the R34 we have in game. FIA’s historic database of old homologation forms was a valuable source of information in putting this one together.

Suspension uses a neat multi-link setup in the front where the steering axis is separate from the links which control bump/rebound motion. Sorta halfway between a strut, Ford's Revoknuckle concept, and a traditional double wishbone. Gives really compact packaging, 100% camber recovery, and a nice steering axis. Cool stuff. Rear is nothing unusual; just a fairly ordinary multi-link design with a lower A-arm. Again, same basic geometry shared with the R34 car.

Engine also has a lot in common with the R34’s RB26 2.6L-turbo straight-6 and is the real killer feature for the car. Early in its racing life, this thing was putting out over 600hp @ 3bar and just destroying the competition. That performance was pegged back somewhat with extra weight and intake restrictors, which is a method we’ve copied here. Two 33mm intake restrictors hold power to ‘just’ 490hp and is near max power in a range all the way from 6000rpm right up to the 8700rpm rev limiter.

Was generous in the aero model and gave it a bit of downforce (very small amount) with modest drag levels. Research showed most comments on the Group A version were that the front makes some lift and the rear wing gives good downforce to the rear, so expect a moderate amount of aero-induced understeer...on top of some mechanical understeer thanks to the strong front bias to weight distribution of 60%. The suspension setup compensates somewhat by being stiff at the rear to encourage low speed oversteer. Interesting combination which is apparently also used by few modern GT3 cars.

Cool thing about these Skylines is that they were, at the heart, RWD and the AWD system was computer controlled to engage a clutch in the center and lock the two axles together only when the rear axle started to lose grip and spin. Our model is set up the same way, just with simple friction and viscous clutch action mimicking all the electronic control in the middle. Funny thing is that Nissan tested the Ferguson system (as in the Lotus 56) early in development of the Skylines as it does mostly what they were after - no lock until axle speed difference is above some threshold - and the system they ended up making basically does the same thing, just with massively more dynamic control where the Ferguson system was fully passive.

Honda 2&4 Concept: Neat to see a concept car that truly works as designed! The reference material Honda provided had great detail of the suspension geometry - including spring and anti-roll bar rates - so that very little guesswork was needed in taking this from experimental concept to something that actually works on track.

Didn't pull any tricks in the suspension design from the CAD reference and it works quite well with the BAC Mono dampers. The simple chassis structure, known mass and known components made it easy to approximate weight distribution at roughly 53% rear and center of gravity height at a mere 30cm above ground without the driver on board. With driver, these number shift to around 53% rear and 28.5cm high thanks to sitting so low and far back in the car. Another neat finding is that the offset chassis and driver position combine to just about cancel each other out for any lateral weight bias. More signs of this as a radical yet functional concept. Nice one, Honda.

The RC213V is a pure MotoGP race engine, which usually brings about some uncertainty as to claims of power level and such, but this one was fairly simple to put together due to the customer versions of the same thing on the market. All research signs point to it being a very strong unit matching the claimed 220hp at 13,500rpm and a fat power band keeping it above 190hp for everything north of 10,500rpm. A VFR1200F DCT does the job of putting that power to the ground through too-skinny rear tires. I say ‘too-skinny’ because 220hp is a lot to manage(!) and, despite 56% rear weight, the rear rubber only has a 51.7% bias in width. It’s still a lot of grip and it is stupid fast - almost on pace with GT3 at Long Beach where top speed isn't vital - while rewarding smooth driving. Don't overcompensate in slides; it'll probably correct itself if you don't add more energy with big inputs. Really fun drive so long as you keep it smooth and let the car do most of the work.

I absolutely love the Honda 2&4 concept. It really is an awesome ride and I'd really like to drive it irl one day... I heard Honda was said to be actually considering to build this thing in a small series.

Thanks for the write-up Casey and your hard work. I would respectfully like to point out a few errors though, regarding the info on the Civic Type-R. In your write up, you seems to be getting a bit confused between the details of the 2015 FK2 Type-R (the one in the game) and the 2017 FK8 Type-R. The FK2 version has torsion beam rear suspension and managed a best of approximately 7:50 around the ring. The FK8 has the improved fully independent rear suspension and set the new fwd record of 7:43 at the ring.

The good news is that your time is much closer to the real life record than you thought, and by a coincidence, is the same as my own PB in the car! Having previously owned the car and now the 2017 version, in my humble opinion, I think you did an impressive job with the car. Thanks.